Abstract A 3D simulation tool for solid oxide fuel cells (SOFCs) was described to simulate the mass, momentum and energy conversions in the mono- block layers built (MOLB)-type SOFC system。 Considering the co-flow and counter-flow cell designs, the temperature distributions, variations of reaction species and current densities of the single-unit cell were calculated under the different working conditions。 The simulation results show that the co-flow case has more uniform temperature and current density distributions。 Similar to the planar SOFC, in co-flow case, increasing fuel delivery rate or hydrogen mass fraction in the fuel, average temperatures of PEN (positive/electrolyte/negative) and current densities rise, but the average temperatures of PEN decrease with increasing the delivery rate of air。 In particular, MOLB-type SOFC has some advantages such as: higher hydrogen utilizations, lower temperature difference and higher current density。 However the current density distributions are less uniform in MOLB-type SOFC, which is a disadvantage in this type SOFC。 84800

© 2007 Published by Elsevier B。V。

Keywords: MOLB-type SOFC; Thermo-fluid model; Electrochemical model; Temperature distribution; Current density

1。Introduction

The solid oxide fuel cell (SOFC) is expected to be a promis- ing alternative power source for distributed or residential power plants because of its higher energy conversion efficiency and power density, lower environmental hazards and production cost [1–3]。 However, the further development of SOFC stacks faces the challenges related to maximize the power density and to minimize the non-uniform temperature distribution, which contributes to the thermal stress in the SOFC components [4,5]。

 At this stage of SOFC stack development, design of geometry

 is almost as crucial as material development。 In the past, some focus has been placed on the designs of new material [6–9] or novel geometry [10–13]。 Besides planar and tubular SOFCs, recently, MOLB-type SOFC also has been drawn keen attention and researched to improve the comprehensive performance of SOFC。 In the MOLB-type SOFC, the corrugated-shaped  PEN

not only ensures the effective electrochemical reaction area is higher than the projected area, but also provides the film with the combined function of fuel and airflow paths, mak- ing the cell compact and saving the laborious work of channel machining。

In addition to the geometrical designs of SOFC, the work- ing conditions, such as delivery rate of gas to the cell system (including the fuel and air gas), and hydrogen mass fraction in fuel gas also influence the performances of SOFC in a com- plicated way。 Therefore, it is difficult and uneconomical to investigate the influences of these parameters independently by testing methods。 The computer simulation technique has been used to analyze effectively the process of energy conversion in the SOFC system。 Some modeling of the SOFC during steady operation has been constructed to calculate temperature and cur- rent density distributions [14–20]。 Investigations of planar and MOLB-type SOFC operation and performance have predicted cell temperature and current density distributions for various flow patterns [21–24]。 However, only a little work has been performed on the influences of the operating conditions on the performances of planar SOFC [25,26], or even saying nothing of the MOLB-type SOFC。

0378-7753/$ – see front matter © 2007 Published by Elsevier B。V。 doi:10。1016/j。jpowsour。2007。06。070

Fig。 1。 Illustrations of the one cell-stack and the single unit model for MOLB- type SOFC。

The objective of present work is to simulate the thermal and electrochemical performances of MOLB-type SOFC。 A computational fluid dynamics (CFD) model tool is demonstrated to predict temperature, species mass fraction and current den- sity distributions in SOFC system。 The results simulated in this paper can not only guide the designer in understanding how geometrical design affects thermodynamics performances and electrochemical characteristics of the SOFC, but also  provide a more reasonable basis for designing geometry and choosing working conditions of the SOFC stacks。